This paper considers how we can evolve the transport protocol stack in
a network that has ossified around TCP and UDP transport, due to the
presence of middleboxes that reject other transport protocols, and
anything other than minor modifications to existing transports.
It observes that future development must be done using the existing
protocols as substrates, always maintaining on-the-wire compatibility,
and that to advance, we must embrace the ossification of the network,
and learn to reinterpret and extend the existing protocols.